Railway signaling system



April 28, 1959 2 Sheets-Sheet 1 Filed Oct. 2a, 1957 Pick ed (go when Sg'yml I5 is cleaned HETFPH April 1959 D. D. HUFFMAN ETAL 2;884,517

RAILWAY SIGNALING SY STEM Filed 0.0%,, 28, 1957 2 Sheets-Sheet 2 la) T J b Pzb'ked zgp when Sly/2d WGTPR 45 (19 cleared. 546R b {W4 1 0mg: 19001 12 41:02 I d 2 m L: Wanna I i i J r INVENTORS Donald D. Huffman and WGZE'IH HTWOZZNE'Y United States PatentfQ 2,884,517 RAILWAY SIGNALING SYSTEM Donald D. Huffman, Penn Township, Allegheny County,

and Edd C. Dwyer, Pittsburgh, Pa., assignors to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application October 28, 1957, Serial No. 692,928 8 Claims. (Cl. 24634) .one end only of the track section without the use of the usual line conductors.

In an application for Letters Patent of the United States, Serial No. 692,927, filed on the same date as this application by Wesley Y. Speight, and assigned to the same assignee, there is shown a coded track circuit arrangement for A.P.B. automatic block signaling in which standard frequency normal codes are used to control wayside signals in one direction and polarized reverse code pulses are used to control the signals in the opposite direction. The standard frequency normal codes used in one direction are the 180, 120 and 75 code frequencies. The 180 and 120 code frequencies are used to control the proceed and approach indications, respectively, of the signals, and the'75 code frequency is used as a carrier for controlling the reverse code pulses when the traffic direction is reverse. The 75 code, as well as no code, results in a stop signal for the direction in which the normal code governs.

The reverse code pulses of said arrangement consist of negative, positive and alternate positive-negative code pulses. Negative reverse code pulses are used to control the stop indication of the signals for overlap purposes, positive reverse code pulses are used to control the caution indication of the signals, and alternate positive-negative reverse code pulses are used to control the proceed indication of the signals.

Our invention consists of a modification of the arrangement of the above mentioned Speight application and the adaptation thereof to manually control opposing absolute signals in a railway traflic controlling system.

One object of our invention is to provide an improved system whereby opposing signals controlling the movement of railway traffic into a section of single track are manually controlled from only one end of the single track stretch.

Another object of our invention is to provide an im proved system of the type described whereby the necessity for line conductors to establish the direction of trafiic is eliminated.

A further object of our invention is to provide in a system of the type described, a method for indicating at the control point the condition-of the signal at'the remote point without the use ofline conductors for transmission of this information.

Other objects and characteristic features of our invention will become apparent as the description proceeds.

In practicing our invention, we accomplish the foregoing objects by a coded track circuit arrangement wherein master or normal code pulses of different frequencies are supplied to the rails of the track section at the remotely controlled signal location, and polarized feedback or reverse code pulses are supplied to the rails of the track section at the manual control point signal location. At the remotely controlled signal location positive normal code pulses at the 180 code frequency are supplied to the rails to control the proceed indication of the signal at the control point; positive normal code pulses at the code frequency are supplied to the rails to control the caution indication of said signahand negative normal code pulses at the 75 code frequency are supplied-to the rails to indicate at the control point that the controlled signal at the remote location is indicating caution or proceed. At the control point, negative code pulses are supplied to the rails for controlling the operation of the apparatus at the remotely controlled signal location; positive code pulses are supplied to the rails to control the caution indication of the remote signal, and alternate positive-negative code pulses are supplied to the rails to control the proceed indication of said signal.

We shall describe one arrangement of railway signaling apparatus embodying our invention, and shall then point out the novel features thereof in claims.

In the drawings, Figs. 1 and 2, arranged side by side with Fig. 1 at the left, show the track plan and circuits associated with a single track section of railway track equipped with apparatus embodying our invention. Fig. 1 shows the apparatus and circuit arrangement at the left-hand or west end of a track section designated by the reference character T and comprising rails designated in and 1b. This end of said track section constitutes the manual control point for the system of our invention. Fig. 2 shows the arrangement of apparatus and circuits at the righthand or east end of said track section. This end of the track section constitutes the remotely controlled signal location.

In order to simplify the description, hereinafter the manual control point location will be referred to as the control location, and the remotely controlled signal location as the remote location.

Referring to Figs. 1 and 2 of the drawings, track section T is separated from the track sections to the left and right thereof by insulated joints designated by the reference character J. Located at the control location or the west end of track section T, adjacent the insulated joints I, are shown traffic controlling devices or signals 18 and 2S. Signal 28 controls the movement of trains into track section T in an eastward direction and is the controlled signal at that point. Signal 18 may be either an automatic or manually controlled signal, the method of its control being immaterial to our invention. This signal is shown because the relay which functions to control it also functions as a part of the control for the signal 35 at the remote location.

Located at the remote location or the east end of track section T adjacent the insulated joints I are traffic controlling devices or signals 38 and 4S. Signal 38 controls the movement of trains into track section T in a westward direction and is the controlled signal at that point. Signal 48 may be either an automatic or manually controlled signal and is shown because the relay which controls it enters into the control of signal 28.

The signals shown may be of any of the well known types but as here shown are of the color-light type. Figs. 1 and 2 show the lighting circuits for signals 23 and 38, respectively, It is not necessary for an understanding of our invention to show the lighting circuits for signals 1S and 48. Signals 2S and 35 are each shown as having three lamps, green, yellow and red designated by the reference characters GE, YE and RE, respectively, prefixed by the number of the signal with which'the lamps are associated. The indications resulting from the green, yellow or red lamps being illuminated individually are proceed, caution, and stop, respectively.

It should be pointed out at this time that a suitable source of control current is provided at each location, this source being preferably a battery of proper voltage and capacity. For the sake of simplicity this current source is not shown in the drawings, the positive and negative terminals of the source being designated by the reference characters B and N, respectively.

Certain of the relays shown in the drawings are of the slow release type, the contacts of such relays being designated slow release by arrows drawn vertically through the movable portion of each contact and with the head of the arrow pointing in the downward direction, that is, the direction in which the relay is slow acting. The slow-release characteristic of these relays is provided by devices usually referred to as snubs, connected across the terminals of the relay winding for delaying the decay of flux through the core of the relays.

Associated with the rails 1a and 1b are and symbols, respectively. When a code pulse of the polarity shown is supplied to the rails, it is considered to be a positive code pulse; and when a code pulse of the polarity opposite to that shown is supplied to the rails, it is considered to be a negative code pulse. This will be more clearly understood later on in this description.

Connected to the rails of the track section at the control location are code detecting devices shown in Fig. 1 as two track relays designated NETR and RETR. These relays are code following relays of the polar biased type and have contacts which are picked up when and only when current flows through the winding of the relay in the direction indicated by the arrow in the relay symbol. As shown in the drawings the positive terminals of relays NETR and RETR are connected to rails 1b and 1a, respectively. The negative terminals of the relays are connected to each other in series. By this arrangement if pulses of the previously described positive codes are applied to the rails, the contacts of relay NETR only will respond thereto, the current flowing through the windings of the relays being in the direction of the arrow in the symbol for that relay and in the opposite direction of the arrow in the symbol for relay RETR. Similarly, if pulses of negative code are applied to rails in and 1b, the contacts of relay RETR only will respond.

At the remote location is shown a similar arrangement of relays NWTR and RWTR. As is apparent from an examination of Fig. 2, the contacts of relay NWTR will respond only to pulses of positive code and the contacts of relay RWTR will respond only to pulses of negative code. It may thus be said that the associated relays NETR and RETR, and NWTR and RWTR are arranged in a series of opposing relationship.

Relay NETR in Fig. 1 is also provided with a mechanically resonant, frequency decoding contact tuned to a predetermined frequency or code rate. This contact is responsive only to the code rate to which it is tuned, that is, the contact will only follow coded energy of a predetermined code rate supplied to the winding of the relay. Such contacts remain in a position of rest, that is, with their movable member closed against their fixed back contact member, when energy of a rate other than that to which they are tuned is supplied to their associated relay winding. The tuned contact on relay NETR, shown in Fig. 1 of the drawings, is contact d. This contact is also identified by the code rate to which it is responsive, that is, by the notation 180 tuned, and by a line drawn through the terminal of the movable member of the contact. The non-tuned contacts of the track relays are responsive to coded energy of any of the usual code rates and alternately close front and back contacts during receipt of coded energy of any such code rate.

Each of the above described track relays may, for

example, be a polar biased relay of a type similar to that shown and described in Letters Patent of the United States No. 2,730,592 issued January 10, 1956, to Andrew Hufnagel for a Code Following Relay With Frequency Decoding Contacts.

Although we have shown in the drawings but one method of code detection and but one method of code frequency detection, it is to be understood that our invention is not limited to the methods shown but any of the well-known methods may be used in practicing our invention without departing from the spirit and scope thereof.

A source of track circuit energy, shown in the drawings as a battery, is provided at each end of track section T. This battery at the west end of the track section is designated WTB and the track battery at the east end of the track section is designated ETB.

Two rates of coding, and 75 pulses per minute, respectively, are supplied by the constantly operating code transmitter relays 180CTR and 75CTR, located at the east end of track section T. The windings of these relays are connected directly to the battery terminals B and N at that location and the relays are thus constantly operating.

The windings of two relays 1HR and 4HR are shown at the signal locations at the west and east ends, respectively, of track section T. These relays are the signal control relays for signals 15 and 45, respectively, but no control circuits for the relays are shown as they form no part of our invention. The relays are noted on the drawings as being energized when their respective associated signals are cleared.

Associated with the code transmitter relays 75CTR and 180CTR is a code transmitter repeater relay WCTPR which alternately connects the track battery ETB and the track relays NWTR and RWTR to the rails of track section T at the east end of said track section. Relay WCTPR is of the magnetic stick type. The contacts are shown in a vertical plane and the left hand or normal contacts become closed when and only when the current flows through the relay winding in the direction indicated by the arrow. The reversal of the current flow results in the closing of the right hand or reverse contacts. Such relays maintain their contacts in the position to which they were last operated when the windings of the relays are deenergized.

A circuit for controlling the contacts of relay WCTPR to their normal position may be traced from battery terminal B through back contact a of track relay RWTR, back contact a of track relay NWTR, front contact a of code transmitter 75CTR, back contact a of relay 4HR, winding of relay WCTPR, and contact a of relay WCTPR in its reverse position to battery terminal N. The flow of current through the relay winding is in the direction of the arrow so that the relay is now operated to move its contacts to their normal position. When code transmitter 75CT closes its back contact a in its periodic operation, the control circuit for relay WCTPR may be traced from battery terminal B through contact a of relay WCTPR in its normal position, the winding of relay WCTPR, back contact a of relay 4HR and back contact a of 75CTR to battery terminal N. The flow of the current through the winding of relay WCTPR is now opposite to the direction of the arrow and relay WCTPR is controlled to move its contacts to their reverse position. It is thus apparent that with back contact a of relay 4HR closed, relay WCTPR periodically operates its contacts between a normal and reverse position at the 75 code rate as the code transmitter 75CT alternately closes its front and back contact a.

Contact a of relay 4HR in the control circuit for relay WCTPR controls the code rate of the coded energy applied to relay WCTPR. Relay 4HR is energized when signal 4S is cleared, and when this relay becomes energized code at the 180 code rate is applied to the winding of relay WCTPR through front contact a of relay 4HR, and contact a of code transmitter 180CT. This energizing circuit for relay WCTPR being similar to that just described for the application of the 75 code to relay WCTPR, no detailed tracing of the circuit is considered necessary. As will be described hereinafter, contact a of relay 4HR selects between the 75 and 180 code rate to provide a caution or proceed indication, respectively, on signal 2 when signal 4 is cleared.

With the parts in the positions shown in Fig. 2, the contacts of relay WCTPR are alternately operated to their normal and reverse positions at the 75 code rate in the manner previously described. Contact b of relay WCTPR alternately connects track battery ETB, and track relays NWTR and RWTR to the rails of track section T.

The circuit for supplying coded track energy to the rails includes contacts c and d of a relay SASR which is the time locking relay for signal 38. The operation of relay 3ASR will be more fully described hereinafter it being sufficient to state at this time that this relay normally occupies its picked-up position.

The circuit for connecting the positive terminal of the track battery to the rails of track section T at the remote location may be traced from the positive terminal of track battery ETB through front contact c of relay 3ASR, and normal contact b of relay WCTPR to rail 1b of track section T. The negative terminal of the track battery is connected to the rails by a circuit which may be traced from the negative terminal of ETB through front contact d of relay SASR to rail 1a of track section T. Thus, when the apparatus is in its normal condition, positive normal pulses of energy at the 75 code rate are supplied to the rails of track section T at the remote location. Similarly, if signal 45 is cleared, relay 4HR being thus picked up, code pulses at the 180 code rate are supplied to the winding of relay WCTPR as previously described, and contact b of relay WCTPR is then operating at the 180 code rate,and positive normal pulses of energy at this code rate are supplied to the rails of track section T, at the remote location, through circuits identical to those previously described for the 75 code rate.

At the control location, track relays NETR and RETR,

and track battery WTB are alternately connected to the rails of track section T, relays NETR and RETR being connected through back contacts of reverse code generating relays RCTPR and NCTPR, and track battery WTB being connected through front contacts of the reverse code generating relays. The track relays NETR and RETR are connected to the rails during the on period of the code being supplied to the rails at the remote location and being received from the rails at the control location. Track battery WTB is connected to the rails during the off period of said code. Referring to Fig. l, the code pulses being received from rail 1b of track section T at the control location are supplied to the windings of track relays NETR and RETR by a circuit which may be traced directly from rail 1b to the positive terminal of track relay NETR. The energy being received from rail 1a of track section T is supplied to the windings of track relays NETR and RETR by a circuit which may be traced from rail 1a through back contact a of relay RCTPR, and back contact a of relay NCTPR to the positive terminal of relay RETR. These code pulses are of the polarity designated as positive code and the flow of current through the winding of relay NETR is such that the contacts of the relay follow the code pulses, alternately making their front and back contacts at the 75 or 180 code rate according to the code frequency being supplied to the rails at the remote location. This code frequency is of the 75 code rate at this time.

In Fig. 1 there is also shown a pole-changing relay designated by the reference character PCR. This relay is of the magnetic stick type, similar to relay WCTPR at theremote location, and under normal conditions, the

6 relay and its contacts occupy their reverse positions, as will be more fully described hereinafter.

With the contacts of track relay NETR following code, a circuit is intermittently completed for applying coded energy to the reverse code generating relay RCTPR. This circuit may be traced from battery terminal B through front contact b of track relay NETR, contact b of relay PCR in its reverse position, and the winding of relay RCTPR to battery terminal N. Relay RCTPR is, therefore, being operated at the same code rate as track relay NETR.

When relay RCTPR is energized during one of the on code periods the previously traced energizing circuit for relay NETR is opened at back contact a of relay RCTPR. However, there is included in the control circuit to relay NETR, in multiple with contacts a of relays RCTPR and NCTPR, a front contact a of relay NETR. This contact provides an alternate energizing path for relay NETR when that relay is picked up and relay RCTPR opens its back contact a. It is not considered necessary to trace this alternate energizing path for relay NETR and it is believed apparent that relay NETR is maintained in its picked up position through said path during the entire length of the on period of coded energy received from the rails. (A contact a of relay RETR is included in the control circuit to that relay to provide an alternate path for maintaining relay RETR picked up when it is picked up by energy of the opposite polarity to that described, that is, by negative code pulses.)

Relays RCTPR and NCTPR are provided with resistor snubs across the terminals of the windings to slightly retard the release of the armatures of the relays. During the off period of the code pulses being received from the rails by relays NETR and RETR a negative reverse code pulse is supplied to the rails of the section. Rail -1a is connected to the positive terminal of track battery WTB through a circuit which may be traced from said positive battery terminal through front contact b of relay RCTPR, back contact a of relay RETR, and back contact a of relay NETR to rail 1a. Rail 1b is connected to the negative terminal of the track battery WTB by a circuit which may be traced from rail 1b through back contact b .of relay NCTPR to the negative terminal of WTB. Thus, during the periods contact a of relay NETR makes its back contact, and relay RCTPR maintains its front contact b closed because of the slow release characteristic of relay RCTPR due to said resist-or snub, pulses of negative reverse code energy are supplied to the rails of track section T.

Front contact repeater of each of the relays NETR and RETR are provided at the control location. The operation of reverse front contact repeater relay RETFPR will be described hereinafter in this description, and the operation of normal front contact repeater relay NETFPR will now be described.

During the code following action of the contacts of relay NETR, a circuit is also completed for supplying coded energy to the normal front contact repeater of said track relay, relay NETFPR. This circuit may be traced from battery terminal B through front contact 0 of relay NETR and the winding of relay NETFPR to battery terminal N. Relay NETFPR is picked up at this time and is maintained picked up by a rectifier snub connected across the terminals of the relay winding. This snub delays the release of the relay, when energy is removed therefrom, for a sufficient length of time to span the open periods of the front contact 0 of relay NETR during the off periods of the positive normal coded energy received from the rails.

Pulses of coded energy are also supplied to a track repeater relay ETPR at this time. This relay is energized when track relay NETR is following pulses of positive normal coded track energy or track relay RETR is following pulses of negative normal coded track energy.

The circuit for energizing relay ETPR when NETR is following pulses of positive normal code may be traced from battery terminal B through back contact of relay NETR, back contact c of relay RETR, front contact c of relay NETFPR, winding of relay ETPR and the 180 code tuned back contact a of relay NETR to battery terminal N. A capacitor-resistor unit designated CR1 is provided for maintaining relay ETPR in the picked up position during the on periods of the coded track pulses, that is, when the back contact 0 of relay NETR is open. This unit is connected in multiple with relay ET PR when either relay NETFPR or RETFPR is energized due to the code following action of relay NETR or RETR, respectively, and receives a storage of energy during the closed periods of back contact c of relays NETR and RETR. The circuit for charging unit CR1 may be traced from battery terminal B through back contact 0 of relay NETR, back contact c of relay RETR, front contact a of relay NETFPR (or front contact b of relay RETFPR) and through the condenser resistor unit and back contact d of relay NETR to battery terminal N. During the open period of back contact c of relay NETR (or back contact c of relay RETR when relay RETR is receiving negative coded track pulses) the charge of energy stored in unit CR1 is discharged through relay ETPR through an obvious circuit and maintains relay ETPR in its picked up position. Upon release of contact a of relay NETFPR (or contact b of relay RETFPR) a circuit is completed to dissipate the energy stored in unit CR1 and cause immediate release of relay ETPR. This circuit may 'be traced from the left hand terminal of unit CR1 through back contact b of relay RETFPR, and back contact b of relay NETFPR to the right hand terminal of unit CR1.

A proceed indication control relay 2DR is provided to control the green lamp of signal 2. This relay is energized by pulses of energy at the 180 code rate by a circuit which may be traced from battery terminal B through the winding of relay 2DR, front contact b of relay ETPR, and 180 tuned front contact d of relay NETR to battery terminal N. Relay 2DR is maintained in a picked up position during the open periods of front contact d of relay NETR by a rectifier snub provided for the winding of relay 2DR. This rectifier iseonneeted to the terminals of the winding of relay 2DR through said front contact b of relay ETPR so that the snub will be effective only so long as the front contact b of relay ETPR remains in its closed position.

A manually operated selector, circuit controller or control lever for controlling signals 25 and 33 at the west and east ends, respectively, of track section T is shown in a conventional manner in Fig. 1. This lever is designated 23CL and, as shown, normally occupies a normal or N position and is operable to right and left or R and L positions, respectively. The lever is operated to its R position for clearing signal 28 for a train movement to the right through track section T, and to its L position for clearing signal 38 for a train movement to the left through said track section. Below the lever are shown a series of circles designated 5 through 11, in elusive, which represent contacts on said control lever. Within each of the circles is one or two letters which designate the position of the lever in which a circuit may be completed through the contact represented 'by the circle. It is to be understood that any type of controller or selector may be used for lever 2-3CL and we do not contemplate the use of any certain type of controller in practicing our invention. It is also to be understood that contacts of remotely controlled relays as in a, C.T.C. system of control may be used in place of the manual lever and its associated contacts.

There is also shown in Fig. 1 a time locking relay '2ASR and a time element relay ZTER. These relays operate in combination to provide a time delay before signal 38 can be cleared, after signal 28 has been cleared and then manually controlled to give a stop indication. These relays and their operation form no part of our invention, but are shown so that the system will be complete. Relay ZASR is normally maintained in a picked up position by a stick circuit which may be traced from 'battery terminal B through contact 11 of signal control lever 2-3CL, closed from the normal to the left position designated NL, front contact a of relay 2ASR and the winding of relay ZASR to battery terminal N. Relay ZASR is also provided with two energizing circuits in multiple. These circuits may be traced from battery terminal B through said contact 11 of lever 2-3CL in its normal to left position, front contact a of relay ZTER or back contact d of relay ETPR, and the winding of relay ZASR to battery terminal N. Relay ZTER is provided with a pick up circuit, when relay ZASR is deenergized, which may be traced from battery terminal B through contact 11 of signal control lever 23CL, back contact a of relay ZASR, and the windnig of relay ZTER to battery terminal N. The operation of relay ZASR and relay ZTER will be more fully described hereinafter.

Signal control relay 2HR shown in Fig. 1 controls the red and yellow lamps of signal 28. This relay is controlled by a circuit which may be traced from battery terminal B through front contact d of relay NETFPR, front contact 0 of relay ETPR, back contact b of relay ZTER, contact 10 of signal control levers 2-3CL, back contact b of relay 2ASR, and the winding of relay 2HR to battery terminal N. Back contact b of relay ZTER is included in the circuit to check that relay ZTER has returned to its normal position, after an operation thereof, before relay 2HR can again be energized and signal 28 again cleared.

All apparatus being considered to be in its normal condition at this time, relay 2HR is in the released position, its control circuit being open at contact 10 of signal control lever 2-3CL and back contact b of relay 2ASR. A circuit is therefore, completed for the illumination of the red signal lamp ZRE of signal 28. This circuit may be traced from battery terminal B through back contact a of relay 2HR, and the filament of the red signal lamp ZRE to battery terminal N.

Several indication lamps TKE, ZGKE, ZRKE, 3GKE and 3RKE, are also illustrated in Fig. 1. While these lamps are shown as being located at the control point at the west end of track section T, it is to be understood that the contacts of the relays used to control the energization of these lamps may also be used to transmit indications to a remote control point if a remote system of control such as a C.T.C. system is to be used in practicing our invention.

Indication lamp TKE is the track occupancy indication lamp and is normally dark. The circuit for illumination of this lamp during track occupancy may be traced from battery terminal B through back contact a of relay ETPR and the filament of lamp TKE to battery terminal N.

Indication lamps ZGKE and ZRKE indicate the condition of signal 28. This signal being normally at stop a circuit is normally closed for illumination of indication lamp ZRKE. This circuit may be traced from battery terminal B through back contact b of signal control relay 2HR and the filament of lamp ZRKE to battery terminal N. When relay 2HR picks up to control signal 25 to a caution or proceed indication, a circuit for illumination of lamp ZGKE may be traced from battery terminal B through front contact b of relay 2HR to the filament of lamp ZGKE to battery terminal N.

Indication lamps SGKE and 3RKE indicate the condition of signal 38. The red indication lamp 3RKE is illuminated by a circuit which may be traced from battery terminal B through back contact a of relay RETFPR and the filament of lamp 3RKE to battery terminal N. When relay RETFPR picks up, as will hereinafter be described, a circuit is closed for illumination of green indication lamp 3GKE. This circuit may be traced from battery ..ing of relay 3ASR to is also provided with 9 terminal B through front contact a of relay RETFPR and the filament of lamp 3GKE to battery tenminal N.

In Fig. 2, the positive terminal of the winding of track relay NWTR is connected to the rail 1b of the track section, during the oif periods of the normal code, through contact b of relay WCTPR in its reverse position. The positive terminal of the winding of relay RWTR is connected directly to rail 1a of the track section. Therefore, during the off periods of the normal code, the circuits are in condition for track relays NWTR and RWTR to receive from the rails the pulses of reverse code being supplied to the rails at the control location, and, these code pulses being negative pulses under normal conditions of the apparatus as shown the contacts of relay RWTR are operated and follow the said code pulses. Back contacts a of relays NWTR and RWTR, in the previously described control circuit of relay WCTPR, insure that relay WCTPR remains in its reverse position for the duration of each reverse code pulse.

The code following action of contact b of track relay RWTR supplies pulses of coded energy to the windings of a reverse front contact repeater relay RWTFPR and a track repeater relay WTPR and these relays pick up. The circuit for the winding of relay RWTFPR may be traced from battery terminal B through back contact b of relay NWTR, front contact b of relay RWTR and the winding of relay RWTFPR to battery terminal N. Relay RWTFPR is provided with a capacitor-resistor unit CR3, connected across the terminals of its winding, to make the relay slow in releasing. This unit delays the release of the relay sufficiently that the relay will remain in its picked-up position during the open periods of front contact b of relay RWTR in its code following operation. (Actually the unit CR3 insures that relay RWTFPR will remain picked up during pulses of alternate negative and positive reverse code, when contact b of relay RWTR closes its front contact only during every other on pulse of'reverse code as will be fully explained hereinafter.)

The circuit forsupplying code pulses to the winding of A track repeater relay WTPR, at this time, may be traced from battery terminal B through back contact b of relay NWTR, back contact b of relay RWTR, front contact b of relay RWTFPR, and the winding of relay WTPR to battery terminal N. Relay WTPR is provided with a capacitor-resistor unit snub CR4 to maintain the relay in its picked up position during the open periods of back contact b of relay RWTR in its code following operation. The capacitor-resistor unit cooperates with relay WT PR in a similar manner to that previously described for capacitor-resistor unit CR1 and relay ETPR in Fig. 1 and no further description is considered necessary.

There is also shown in Fig. 2 the aforementioned time locking relay 3ASR and a time delay relay 3TER. These relays operate in combination to provide a time delay before signal 28 can be cleared, after signal 35 has been cleared and then manually controlled to display its stop indication. As with relays ZASR and ZTER for signal 2, these relays and their operation form no part of our invention, but are shown merely so that the system will be complete. Relay 3ASR is normally maintained in a picked up position by a stick circuit which may be traced from battery terminal B through back contact a of signal control relay 3HR for signal 35, back contact e of relay NWTFPR, front contact a of relay 3ASR, and the windbattery terminal N. Relay 3ASR two energizing circuits in multiple. These circuits may be traced from battery terminal B through said back contact a of relay 3HR, back contact e of relay NWTFPR, front contact a of relay 3TER or back contact b of relay WTPR, and the winding of relay 3ASR to battery terminal N. Relay 3TER is provided with a pick up circuit, when relay SASR is deenergized, which may be traced from battery terminal B through back contact a of relay 3HR, back contact e of relay NWTFPR, back contact a of relay 3ASR, and the wind- 10 ing of relay 3TER to battery terminal N. The operation of relay SASR and relay 3TER will be more fully set forth later on in this description.

Signal control relay 3HR shown in Fig. 2 controls the red and yellow lamps of signal 3. This relay is controlled by a circuit which may be traced from battery terminal B through back contact b of relay 3TER, back contact b of relay SASR, front contact a of relay WTPR, front contact d of relay NWTFPR and the winding of relay 3HR to battery terminal N. Back contact b of relay 3TER is included in the circuit to check that relay 3TER has returned to its normal position, after an operation thereof, before relay 3HR can again be energized and signal 38 again cleared.

All apparatus being considered to be in its normal condition at this time, relay 3HR is in the released position, its control circuit being open at contact d of relay NWTFPR and contact b of relay 3ASR. A circuit is therefore completed for the illumination of the red signal lamp 3RE of signal 38. This circuit may be traced from battery terminal B through back contact b of relay SHR and the filament of the red signal lamp 3RE to battery terminal N.

We have described above the condition and operation of the apparatus under normal conditions and will now describe its operation when signal 25 is to be cleared for a train movement in an eastward direction over the track section.

The operator at the control location moves the control lever 2-3CL for signal 2 towards its R position. The movement of signal lever 2-3CL away from its N position opens, at its contact 11 the energizing circuit for relay ZASR and this relay becomes released, closing its back contacts a and b. The closing of back contact b of relay ZASR and the completion of the movement of lever 2-3CL to its R position, closes the previously traced circuit for energization of relay 2HR, relays NETFPR and ETPR already being in their picked up positions as previously described.

The energization of relay 2HR opens at its back contact a the previously traced circuit for illumination of red signal lamp ZRE and closes a circuit for illumination of yellow signal lamp ZYE. This circuit may be traced from battery terminal B through front contact a of relay ZHR, back contact a of relay 2DR (assuming normal code at the 75 code rate is being received from the track rails), and the filament of yellow signal lamp ZYE to battery terminal N. If the normal code pulses being received from the track rails are at the code rate due to signal 48 being in the clear position as previously set forth, relay 2DR will also be picked up and a circuit will be completed for illumination of green signal lamp 2GB. This circuit may be traced from battery terminal B through front contact a of relay ZHR, front contact a of relay ZDR, and the filament of green signal lamp 2GB to battery terminal N.

The energization of relay ZHR, as described above, opens the previously traced circuit to red indication lamp ZRKE at back contact b of relay ZHR, thereby extinguishing that lamp, and closes the previously traced energizing circuit for green indication lamp 2GKE at front contact b of relay 2HR. An indication is thus given to the operator that signal 28 is cleared.

The closing of back contact a of relay ZASR, under the above described conditions, prepares the energizing circuit for relay ZTER. If the operator manually controls signal 28 to stop, before the signal is accepted by a train, the circuit is completed for energization of relay ZTER, through contact 11 of signal control lever 2-3CL, and relay 2TER begins its timing cycle. After the expiration of the timing period, front contact a of relay ZTER closes and, completes an energizing circuit, previously described, for relay ZASR. Relay 2ASR picks up, opening its back contact a in the energizing circuit to relay ZTER and closing its stick circuit through its own front contact a. The opening of back contact a of relay ZASR deenergizes relay 2TER, which thereupon releases, and all apparatus is again in the normal condition. As previously stated, back contact b of relay ZTER, in the control circuit of relay 2HR, checks that relay ZTER has returned to its normal position.

We 'will now assume that signal 28 has been cleared for an eastward train movement over track section T and a train accepts the signal, moving past signal 25 into said track section. The shunting of the rails of track section T, shunts the normal code pulses being transmitted from the remote location and deenergizes the winding of track relay NETR. Relay NETR, and consequently relay RCTPR, cease following code; and relays NETFPR, ETPR and, if 180 code is being received at this time, relay 2DR, all release, due to the cessation of the coding action of the contacts of relay NETR. The opening of front contacts and d of relays ETPR and NETFPR, respectively, opens the control circuit to relay 2HR and that relay also releases. The closing of back contact a of relay ETPR completes the previously described energizing circuit for track occupancy indication lamp TKE and that lamp is illuminated to indicate to the operator that the track section is occupied. If, after the acceptance of signal 28 by the train, the operator moves signal control lever 23CL to its normal position, the previously described energizing circuit for relay ZASR becomes closed at back contact d of relay ETPR and contact 11 of control lever 2-3CL, and relay ZASR picks up. It is thus not necessary to operate the time element relay ZTER, at this time, to energize relay ZASR,

The deenergization of relay 2HR also opens the control circuit to the green or yellow signal lamps 2GB or 2YE and again closes the circuit to red signal lamp ZRE to cause signal 28 t6 display its stop indication.

At the east end of track section A, relay RWTR receives no reverse code pulses due to the cessation of operation of relay RCTPR and the track shunt, and that relay ceases to follow code. However, relay WCTPR continues to operate at the 75 or 180 code rate and supply the pulses of normal code to the rails. These code pulses will reset the operation of the apparatus when the track section is vacated by the train.

Relay RWTR, having ceased to follow the pulses of the reverse code formerly received from the rails, relay RWTFPR and consequently relay WTPR will release, due to the cessation of the coding action of contact b of relay RWTR. No other operation of the apparatus shown in Fig. 2 takes place at this time.

When the train vacates track section T, the code pulses, being supplied to the rails by the coding action of relay WCTPR at the east end of the section, are again received by relay NETR at the west end of the track section and all apparatus 'will return to its normal condition, previously described.

We will now assume that signal 1 is at stop, and relay IHR is deenergized due to some condition in advance of signal 1, and that, under these conditions, the operator desires to clear signal 3 for a westward train movement through track section A. As previously stated the contacts of relay PCR shown in Fig. 1 normally occupy their reverse or right hand position. The control circuit for so positioning the contacts of this relay may be traced from battery terminal B through contact 7 of lever 2-3CL, which remains closed from the normal to the right hand position, back contact d of relay NCTPR, contact a of relay PCR in its normal position, Winding of relay PCR, and back contact 0 of relay RCTPR to battery terminal N. The direction of current through the relay at this time being in a direction opposite to that of the arrow on the relay symbol, the contacts of the relay will be operated to their reverse or right hand position as shown. The movement of contact a of relay PCR to its reverse position opens the above described control circuit for relay PCR. However, any time the remainder of the apparatus in Fig. 2 returns to its normal condition and the contacts of relay PCR occupy their normal position, the relay is immediately controlled by the above traced circuit to cause the relay contacts to occupy their reverse position.

The operator, in order to clear signal 35 as stated above, moves signal control lever 2-3CL from its normal position N towards its left hand position L. This manipulation opens, at contact 7 of lever 23CL, the above traced circuit for control of relay PCR. The completion of the movement of lever 2-3CL to its left hand position L, prepares a control circuit through contact 6 of lever 2-3CL for operating the contacts of relay PCR to their left hand or normal position. When relay NETR releases on the next ofl period of code from the rails, relay RCTPR remains momentarily picked up as previously described. Thus, when relay NETR closes its back contact b, the circuit is completed for controlling the contacts of relay PCR to their normal or left hand position. This circuit may be traced from battery terminal B through back contact b of relay NETR, back contact b of relay RETR, contact 6 of relay 2-3CL in its L position, front contact 0 of relay RCTPR, 'winding of relay PCR and contact a of relay PCR to battery terminal N. The direction of current through relay PCR at this time, being in the direction of the arrow on the relay symbol, the contacts of relay PCR move to their normal position. The previously described circuit for controlling relay PCR to move its contacts to their reverse position being open at contact 7 of lever 2-3CL, said contacts remain in their normal position at this time.

Contact b of relay PCR, moving to its normal position opens the previously described control circuit for relay RCTPR ,and closes a control circuit for relay NCTPR. This circuit may be traced from battery terminal B through front contact b of relay NETR, contact b of relay PCR in its normal position, contact 5 of leve'r' 2-3CL in the L position, front contact c of relay 2ASR and the winding of relay NCTPR to battery terminal N. Front contact 0 of relay 2ASR is included in the control circuit for relay NCTPR, so that relay NCTPR cannot operate to apply positive reverse code pulses to track section T, when lever 2-3CL has 'been moved to its L position and relay ZASR occupies its released position. Relay ZASR may be in its released position because sig; nal 28 is in time, that is, because signal 28 has been cleared, and then manually controlled to stop, and relay ZTER is operating. It is thus insured that relay NCTPR cannot apply positive reverse code pulses to track section T and operate signal 3 to display a clear indication, until relay ZASR is in its normal or picked up position.

The closing of the above traced control circuit to relay NCTPR causes that relay to follow the code operation of contact I) of track relay NETR and code pulses of positive reverse code are supplied to the rails of track section T. The positive terminal of track battery WTB is intermittently connected to rail In by a circuit which may be traced from said positive terminal through front contact 0 of relay NCTPR to rail 1b of track section T. The negative terminal of the track battery is intermittently connected to rail 1a by a circuit which may be traced from said battery terminal through front contact b of relay NCTPR, back contact a of relay RETR, and back contact a of relay NETR to rail 10 of track section T. It is obvious that the pulses of reverse code being supplied to the rails of track section T are of the opposite polarity to those previously supplied to said rails. These pulses are termed positive reverse code as previously set forth.

At the remote location relay NWTR receives the pulses of positive reverse code, which have replaced the negative reverse code pulses formerly being received, the contacts of relay RWTR cease following code and the contacts of relay NWTR start following the positive reverse code pulses. The previously traced control circuit for relay RWTFPR is opened at contact b of relay RWTR and the control circuit for relay NWTFPR is intermittently closed at front contact b of relay NWTR. Relay NWTFPR picks up and is maintained picked up, during the open periods of said front contact b in their code following action, by the capacitor-resistor unit snub CR2 connected across its windings.

The picking up of relay NWTFPR opens at back contact e of relay NWTFPR the previously traced control circuit for relay 3ASR which releases. Relay NWTFPR picking up, prepares at its front contact d the previously described energizing circuit for relay SHR and when relay 3ASR closes its back contact b said energizing circuit is completed and relay 3HR picks up. The previously traced circuit through back contact b for illumination of the red signal lamp 3RE of signal 38 is opened and a circuit is closed for illumination of the yellow signal lamp. This latter circuit may be traced from battery terminal B through front contact b of relay 3HR, front contact 0, of relay NWTFPR, back contact of relay RWTFPR and the filament of the yellow signal lamp 3YE to bat tery terminal N. Signal 38, thus gives a caution indication for a westward train movement into track section T.

The release of relay 3ASR, as described above, causes coded track circuit energy of opposite polarity, to that previously being transmitted, to be supplied to the rails of track section T. The positive terminal of track battery ETB is connected to rail 1a through a circuit which may be traced from said terminal through back contact d of relay 3ASR to rail 1a. The negative terminal of ETB is intermittently connected to rail 1b through a circuit which may be traced from said terminal through back contact c of relay SASR and contact b of relay WCTPR when in its normal position, to rail 1b.

At the control location the contacts of track relay NETR cease following the coded track circuit pulses and the contacts of relay RETR begin to follow said pulses. The control circuit for relay NETFPR is opened at contact 0 of relay NETR and relay NETFPR releases. A circuit is closed for intermittently energizing relay RETFPR and this relay picks up. This circuit may be traced from battery terminal B through back contact 0 of relay NETR, front contact c of relay RETR and the winding of relay RETFPR to battery terminal N. The picking up of relay RETFPR opens, at back contact a of said relay, the previously traced energizing circuit for illumination of indication lamp 3RKE and closes at front contact a of relay RETFPR the circuit for illumination of indication lamp SGKE. An indication is thus given to the operator that signal 38 has cleared.

We will now assume that relay llHR at the control location picks up, the condition which caused it to be released 'being removed, and signal 15 thus displays a clear indication. Signal 38 should, therefore, progress from its yellow indication and gives its green indication.

This is accomplished in the following described manner.

The picking up of relay IHR closes at front contact a of said relay, a second control circuit for relay PCR. This circuit may be traced from battery terminal B through back contact b of relay NETR, back contact b of relay RETR, contact 9 of control lever 2-3CL closed in its L position, front contact a of relay lHR, front contact 0! of relay NCTPR, contact a of relay PCR in its normal position, the winding of relay PCR and back contact 0 of relay RCTPR to battery terminal N. This circuit, being in a direction opposite to that of the arrow shown in the relay symbol, will control relay PCR to cause. that relay to close its reverse contacts. The apparatus at the control location will operate in a manner to supply alternate positive and negative reverse code pulses to the rails of track section T. That is, a pulse of positive reverse code will be supplied to the rails during one off 'period'of the normal'code pulses and a pulse of negative 14 reverse code will be supplied to the rails during the next off period of said normal code, these pulses alternating during each successive pulse of normal code.

The operation of the apparatus to supply to the rails of track section T the said alternate pulses of reverse code is as follows. Relay NCTPR assumed to be picked up during an on period of normal code, the closing of back contact b of relay RET R during the off period of said normal code will control relay PCR to close its reverse contacts. At the next on period of normal code relay RCTPR will be picked up through contact b of relay PCR and relay PCR will be controlled to close its normal contacts during the next off period of the normal code. At the next on period of normal code relay NCTPR will be picked up and relay PCR will again be controlled to close its reverse contacts during the next off period of normal code. Thus, alternate successive operation of reverse code generating relays NCTPR and RCTPR will result, and alternate positive and negative reverse code pulses are supplied to the rails of track section T through contacts b and c of relay NCTPR and contact b of relay RCTPR.

At the remote location relay RWTFPR is picked up through its previously traced control circuit, and relays NWTFPR, WTPR and consequently relay SHR being already up, the previously traced energizing circuit for illumination of signal lamp SYE is opened at back contact c of relay RWTFPR and the lamp is extinguished. A circuit is closed for energizing and illumination of signal lamp 3GB which may be traced from battery terminal B through front contact b of relay 3HR, front contact 0 of relay NWTFPR, front contact 0 of relay RWTFPR and the filament of lamp 3GB to battery terminal N. Signal 35 now gives its proceed indication.

When a westward train accepts signal 38 and enters track section T, both the normal and reverse coded track circuit energies are shunted and, at the remote location, relays NWTR and RWTR cease to follow code and relays NWTFPR, RWTFPR, WTPR and 3HR are released. The circuit for energization of the green signal lamp 3GB is opened and the circuit for energization of the red signal lamp SRE is closed. The signal 38 gives its stop indication again.

The closing of back contact b of relay WTPR, back contact e of relay NWTFPR and back contact a of relay 3HR closes the previously traced energizing circuit for relay 3ASR and that relay picks up. The closing of front contacts 0 and d of relay 3ASR pole changes the circuit for applying the normal code to the rails of track section T and, if the operator at the control location moves the control lever 2-3CL to its normal position, all apparatus will return to its normal condition when the train vacates track section T.

When the aforesaid train accepts signal 38 and enters track section T, relays RETR, NCTPR and RCTPR at the control location cease their code following action, and relays RETFPR and ETPR release. The circuit for indication lamp SGKE is opened and the lamp is extinguished. The circuit for indication lamp SRKE is closed and that lamp is illuminated. Also the circuit for track occupancy indication lamp TKE is closed and that lamp is illuminated to indicate track occupancy. The cessation of the operation of relays NCTPR and RCTPR also removes the positive and negative pulses of reverse code from the rails. When the aforesaid train vacates track section T, if the operator has previously moved control lever 2-3CL to its normal position, all apparatus will return to its previously described normal condition.

If the operator at the control location clears signal 35, as heretofore described, and then manually controls that signal to stop before it is accepted by a train, relay 3ASR at the remote location would be released, and relay WTPR would not close its back contact b to close the energizing circuit for relay 3ASR. However, relay NWTFPR and consequently relay 3HR would release when signal control lever 2-3CL is moved to its normal position, and the previously described energizing circuit for relay 3TER is closed through back contacts e and a of relays NWTF PR and SHR, respectively. Relay 3TER picks up at the expiration of its predetermined time delay period and the pick up circuit for relay 3ASR is completed over front contact a of relay 3TER. Relay 3ASR picks up, closes its stick circuit over its own front contact a and opens the energizing circuit over its back contact a to relay 3TER. Relay 3TER is thus again released. The back contact b of relay 3TER in the control circuit for relay 3HR checks that relay 3TER is completely released before signal 38 can again be cleared.

Under the above described manipulation by the operator, contacts c and d of relay 3ASR maintain the normal coded track circuit energy in its pole changed condition until relay 3ASR is picked up. It is thus insured that signal 28 cannot be cleared until the time delay has expired and relay 3ASR is picked up. When relay 3ASR again picks u normal coded track circuit energy of the correct polarity for clearing of signal 28 is supplied to the rails of track section T and that signal can be cleared if the operator so desires.

From this description it is apparent that, with apparatus of our invention arranged as shown in Figs. 1 and 2 of the drawings, a system is provided whereby signals, for controlling the movement of trafiic in both directions through a section of single track, can be controlled from one control location without the use of line conductors. It is also apparent that the condition of track occupancy of the track section and the condition of the remote signal can be indicated at the control location without the use of line conductors.

Although we have herein shown and described only one form of apparatus embodying our invention, it will be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

1. In a two-direction single track manual control signaling system, in combination, a section of railway track extending between a first location and a second location, manual control means at said first location for controlling the direction of traffic through said track section, means for supplying coded energy at two or more code rates and of a first relative polarity to said track section at said second location when said manual control means occupies a first or second position; means for supplying feedback code of said second relative polarity to said track section at said first location during the OE periods of coded energy supplied to said track section at said second location, when said manual control means occupies said first or second position and said track section is unoccupied by a train; means for supplying feedback code of said first relative polarity to said track section at said first location during the off periods of coded energy supplied to said track section at said second location, when said manual control means occupies a third position, trafiic conditions in the track stretch next to said first location assume a first condition and said track section is unoccupied; means for supplying alternate feedback codes of said first and second relative polarities to said track section at said first location during alternate 01f periods of coded energy supplied to said track section at said second location, when said manual control means occupies said third position, trafiic conditions in the track stretch next to said first location assume a second condition, and said track section is unoccupied; and means for supplying coded energy of said second relative polarity to said track section at said second location when said manual control means occupies said third position and said track section is unoccupied.

2. In combination with a section of railway track extending between a first location and a second location; a first and second traflic controlling device at said first and second locations respectively for governing the movement of trains over said track section and each capable of displaying a stop indication, a caution indication and a proceed indication; manual control means at said first location for controlling said traffic controlling devices and having first, second and third positions; means at said second location for supplying to the rails of said track section pulses of energy of a first certain relative polarity at a first or second code rate in accordance with trafiic conditions to the rear of said second trafiic controlling device and when said trafiic controlling device displays its said stop indication, and for supplying to the rails of the track section pulses of energy of a second certain relative polarity opposite to said first certain relative polarity when the traffic controlling device displays its caution or proceed indication; a first and second code following means at said second location connected to the rails of said track section during the off periods of said pulses of energy supplied to the rails of said track section, said first code following means being responsive only to pulses of energy of a first predetermined relative polarity and said second code following means being responsive only to pulses of energy of a second predetermined relative polarity opposite to said first predetermined relative polarity; means at said second location responsive, when said second code following means is operating, in a manner to control said second traffic controlling device to display its said caution indication; means at said second location responsive, when said first and second code following means are alternately operating, in a manner to control said second trafiic controlling device to display its said proceed indication; means at said first location for supplying to the rails of said track section, when said manual control means occupies its said first or said second position and during the off periods of said pulses of energy supplied to the rails of said track section at said second location, pulses of energy of said first predetermined relative polarity; means at said first location for supplying to the rails of said track section, when said manual control means occupies its said third position and during the off periods of said pulses of energy supplied to the rails of said track section at said second location, pulses of energy of said second predetermined relative polarity or alternate pulses of said first and second predetermined polarities in accordance with trafiic conditions to the rear of said first trafiic controlling device; a first and second code following means at said first location connected to the rails of said track section during the on periods of said pulses of energy of said certain relative polarities, said first code following means being responsive only to pulses of energy of said first certain relative polarity and said second code following means being responsive only to pulses of energy of said second certain relative polarity; means responsive when said first code following means at said first location is operating at said first code rate, for controlling said first trafiic controlling device to display its said caution indication; means responsive, only when said first code following means at said first location is operating at said second code rate, for controlling said first trafiic controlling device to display its said proceed indication; and means at said first location for indicating the condition of said traffic controlling device at said second location, said means being energized only when said second code following means at said first location is operating.

3. In a railway traffic controlling system, in combination, a section of railway track extending between a first location and a second location; means at said second location for supplying to the rails of said track section first pulses of energy of a certain polarity at a first code rate, second pulses of energy of said certain polarity at a second code rate, or third pulses of energy of a polarity opposite to said certain polarity; pulse responsive means at said first location for receiving from the rails of said track section said pulses of energy; first, second and third relay means in conjunction with said pulse responsive means, said first relay means being responsive to said first and second pulses of energy, said second relay means being responsive to said third pulses of energy, and said third relay means being responsive only to said second pulses of energy; means at said first location for supplying to the rails of said track section, during the off periods of said pulses of energy supplied to said rails at said second location, first pulses of energy of a predetermined polarity, or second pulses of energy of a polarity opposite to said predetermined polarity, or said first and second pulses of energy alternately during each successive ofl period of pulses of energy supplied to said rails at said second location; pulse responsive means at said second location for receiving from the rails of said track section said pulses of energy supplied to the rails at said first location; first and second relay means in conjunction with said pulse responsive means at said second location, said first relay means being responsive only to said first pulses of energy of a predetermined polarity, said second relay means being responsive only to said second pulses of energy of a polarity opposite to said predetermined polarity, and both said first and second relay means being responsive to said alternate first and second pulses of energ manual control means at said first location for controlling said pulses of energy supplied to the rails of said track section at said first location, and traflic controlling devices at said first and second locations, said devices being controlled in accordance with said pulses of energy supplied to said track section.

4. In combination with a section of railway track extending between a first location and a second location and over which trains may travel in either direction; a first and second signal each capable of giving stop, caution and proceed indications for governing movement of trains over said track section and located at said first and second locations respectively; a manual control means provided 'at said first location and having first, second and third positions; means provided at said first location for indicating that said second signal is giving its stop indication, or said caution or proceed indication; code detecting means connected to the rails of said section at each said location, each said means having first apparatus in conjunction therewith responsive only to pulses of energy of a first polarity and second apparatus in conjunction therewith responsive only to pulses of energy of a second polarity opposite to said first polarity, and said means at said first location having third apparatus in conjunction therewith responsive only to pulses of energy of said first polarity of a predetermined code frequency; means for supplying to the rails of said section at said second location when said second signal is giving said stop indication, pulses of energy of said first polarity and of a first or second code frequency, said code frequency being selected in accordance with traflic conditions to the rear of said second signal; means for supplying to the rails of said section at said second location when said second signal is giving said caution or proceed indication, pulses of energy of said second polarity; a first relay means energized only when said first apparatus at said second location is operating, a second relay means energized only when said second apparatus at said second location is operating, a third relay means energized when either said first or second apparatus at said second location is operating, a fourth relay means energized only when said second and third relay means are energized; means for controlling said indications of said second signal in accordance with the energized condition of said first, second and fourth relay means; means for supplying to the rails of said section at said first location during the said second location, pulses of energy of said second polarity when said manual control means occupies said first or second position; means for supplying to the rails of said section at said first location during the off periods of pulses of energy supplied to the rails at said second location, pulses of energy of said first polarity or alternate pulses of energy of said first and second polarities, when said manual control means occupies said third position, said pulses being selected in accordance with traffic conditions to the rear of said first signal; a first relay means energized only when said first apparatus at said first location is operating, a second relay means energized only when said second apparatus at said first location is operating, a third relay means energized when either said first or second apparatus at said first location is operating, a fourth relay means energized when said third apparatus at said first location is operating and said third relay means at said first location is energized, a fifth relay means energized when said first and third relay means at said first location are energized and said manual control means occupy said second position; means controlled by said second relay means at said first location, according as the relay means is deenergized or energized for indicating that said second signal is giving said stop indication, or said caution or proceed indication respectively; and means for controlling said indications of said first signal in accordance with the energized condition of said fourth and fifth relay means at said first location.

5. In a railway signaling system, in combination, a section of railway track extending between a first location and a second location; a first and second signal at said first and second locations respectively for governing the movement of trains over said track section and each capable of giving a stop indication, a caution indication and a proceed indication; means at said second location for supplying to the rails or" said track section, when said second signal gives said stop indication; a first master code consisting of pulses of energy of a certain polarity at a first code rate or a second master code consisting of pulses of energy of said certain polarity at a second code rate, selection between said master codes being in accordance with traffic conditions in the rear of said second signal, and for supplying to the rails of said track section, when said second signal gives said caution or proceed indications, a third master code consisting of pulses of energy of a polarity opposite to said certain polarity; manual control means at said first location and having three positions; means at said first location for supplying to the rails of said track section, during the off periods of said master codes and when said manual control means occupy a first or second position, a first feedback code consisting of pulses of energy of a predetermined polarity; means at said first location for supplying to the rails of said track section, during the o periods of said master codes and when said manual control means occupy a third position, a second feedback code consisting of pulses of energy of a polarity opposite to said predetermined polarity, or a third feedback code consisting of alternate first and second feedback codes during alternate oft periods of said master codes, selection between said second and third feedback codes being in accordance with trafiic conditions to the rear of said first signal; a first code detecting means connected to the rails of said track section at said first location and responsive only to said first or second master codes, a second code detecting means connected to the rails of said track section at said first location and responsive only to said third master code, a first relay means at said first location energized only when said first code detecting means is operating, a second relay means at said first location energized only when said second code detecting means is operating, a third relay means at said first location energized when either said first or second code detecting means is operating, a fourth relay means at said first location energized only oft periods of pulses 'of energy supplied to the rails at 7 when said first code detecting means is responding to said second master code and when said third relay means is energized, a fifth relay means at said first location energized only when said manual control lever occupies said second position and said first and third relay means are energized, means for controlling said first signal to give said stop indication when said fifth relay means is deenergized, means for controlling said first signal to give said caution indication when said fifth relay means is energized and said fourth relay means is deenergized, means for controlling said first signal to give said proceed indication when said fourth and fifth relay means are energized; first and second indicating means at said first location for indcating the condition of said second signal, said first or second indicating means respectively being energized according as said second relay means are energized or deenergized; a third code detecting means connected to the rails of said track section at said second location and responsive only to said first or third feedback codes, a fourth code detecting means connected to the rails of said track section at said second location and responsive only to said second or third feedback code, a sixth relay means at said second location energized only when said third code detecting means is operating, a seventh relay means at said second location energized only when said fourth code detecting means is operating, an eighth relay means at said second location energized when either said third or fourth code detecting means is operating, a ninth relay means at said second location energized only when said seventh and eighth relay means are energized, means for controlling said second signal to give said stop indication when said ninth relay means are deenergized, means for controlling said second signal to give said caution indication when said ninth and seventh relay means are energized and said sixth relay means are deenergized; and means for controlling said second signal to give said proceed indication when said ninth, seventh and sixth relay means are all energized.

6. In combination with a section of railway track extending between a first location and a second location, a traffic controlling device at each said location for governing the movement of trains over said section and each capable of giving a stop indication and a first or second clear indication; manual control means at said first location for controlling said devices and having first, second and third positions; means at said second location for normally supplying to the rails of said section pulses of energy of a certain relative polarity at a first or second code rate in accordance with trafiic conditions to the rear of said trafiic controlling device at said second location, a first code following means at said first location responsive only to said pulses of energy of said certain relative polartiy being supplied to the rails of said section at said second location, means at said first location for supplying to the rails of said section pulses of energy of a predetermined relative polarity when said manual control means occupies said first or second positions and during the off periods of said pulses of energy being supplied to the rails of the section at said second location, a first code following means at said second location responsive only to said pulses of energy of a predetermined relative polarity being supplied to the rails of said section at said first location; means at said first location for supplying to the rails of said section pulses of energy of a polarity opposite to said predetermined relative polarity when said manual control means occupies said third position, when trafiic conditions to the rear of said trafiic controlling device at the first location constitute one condition and during the OE periods of said pulses of energy being supplied to the rails of the section at said second location; a second code following means at said second location responsive only to said pulses of energy of a polarity opposite to said predetermined relative polarity supplied to the rails of said section at said first location; means operating at said first location to supply to the rails of said section alternate pulses of said predetermined relative polarity and of said polarity opposite to said predetermined relative polarity when said manual control means occupies said thrid position, when traflic conditions to the rear of said traffic controlling devices at the first location constitute another condition, and during alternate off periods of said pulses of energy being supplied to the rails of the section at said second location; means operating at said second location, when said second code following means only at the second location is following code, to control said trafiic controlling device at the second location to give its first clear indication; means operating at said second location, when said first and said second code following means at the second location are following code, to control said trafiic controlling device at the second location to give its second clear indication; nieans at said second location for'supplying to the rails of said section pulses of energy of a polarity oppcsite to said certain relative polarity when said traffic controlling device at said second location is controlled to give its first or second clear indication, a second code following means at said first location responsive only to said pulses of energy of said polarity opposite to said certain relative polarity; and means operating at said first location, responsive only when said second code following means at the first location is following code, to indicate the condition of said trafiic controlling device at said second location.

7. In a railway trafiic controlling system, in combination, a section of railway track extending between a first location and a second location; a first and second signal at said first and second locations respectively for governing the movement of trains over said track section and each capable of giving a stop indication, a caution indication or a proceed indication; a three-position traffic selective device at said first location; code generating means at said second location for supplying to the rails of said section when said second signal gives said stop indication pulses of energy of a first relative polarity and of a first or second code frequency, said frequency being selected in accordance with trafiic conditions in the track stretch next to said second location, and said means operating, when said second signal gives said caution or proceed indication, to supply to the rails of said section pulses of energy of a second relative polarity opposite to said first certain relative polarity; a first code following relay means connected to the rails of said track section at said second location, said relay means comprising a first relay and associated contacts responsive only to pulses of energy of said first relative polarity and a second relay and associated contacts responsive only to pulses of energy of said second relative polarity opposite to said first relative polarity; a first normal front contact repeater relay energized when said contacts of said first relay of said first code following relay means are operating, a first reverse front contact repeater relay energized when said contacts of said second relay of said first code following relay means are operating, a first track repeater relay energized when contacts of either said relay of said first code following relay means are operating, a signal control relay energized when said first normal front contact repeater relay and said first track repeater relay are energized; circuits through contacts of said signal control relay, said first normal front contact repeater relay and said first reverse front contact repeater relay so arranged that said second signal gives said stop indication when said signal control relay is deenergized, said caution indication when said signal control relay and said first normal front contact repeater relay are energized and said first reverse front contact repeater relay is deenergized, and said proceed indication when all three last mentioned relays are energized; a second code following relay means connected to the rails of said track section at said first location, said relay means comprising a first relay and associated contacts responsive only to pulses of energy of said first relative polarity, a selected one of said contacts being responsive only to pulses of energy of a selected one of said first or second code frequencies, and a second relay and associated contacts responsive only to pulses of energy of said second relative polarity opposite to said first relative polarity; a pole-changing relay having normal and reverse positions at said first location, said relay occupying said reverse position when said traffic selective device occupies a first or second position; a slow release negative code transmitter relay at said first location energized when said pole-changing relay occupies said reverse position and said second code following relay means are energized, means for supplying to the rails of said track section at said first location pulses of energy of said second relative polarity when said second code following relay means are deener-gized and said negative code transmitter relay is picked up; means for controlling said pole-changing relay to said normal position when said traffic selective device occupies a third position, said negative code transmitter relay is picked up and said second code following relay means is deenergized; a slow release positive code transmitter relay at said first location energized when said pole-changing relay occupies said normal position, said second code following relay means are energized and said traffic selective device occupies said third position; means for supplying to the rails of said track section at said first location pulses of energy of said first relative polarity when said second code following relay means are deenergized and said positive code transmitter relay is picked up; means operating in accordance with traflic conditions in the track stretch next to said first location, when said traffic selective device occupies said third position and said second code following relay means are deenergized, to control said pole-changing relay alternately to said normal and reverse positions during alternate off intervals of said pulses of energy supplied to the rails of said track section at said second location; a second normal front contact repeater relay at said first location energized when said contacts of said first relay of said second code following relay means are operating, a second reverse front contact repeater relay at said first location energized when said contacts of said second relay of said second code following relay means are operating, a second track repeater relay at said first location energized when contacts of either said relay of said second code following relay means are operating, a proceed signal indication control relay at said first location energized when said second track repeater relay is energized and said selected one of said contacts associated with said first relay of said second code following relay means is operating, a caution signal indication control relay at said first location energized when said second normal front contact repeater relay and said second track repeater relay are energized and said traflic selective device occupies said second position; circuits through contacts of said caution signal indication control relay and said proceed signal indication control relay, so arranged that said first signal gives said stop indication when said caution signal control relay is deenergized, said caution indication when said caution signal indication control relay is energized and said proceed signal indication control relay is deenergized, and said proceed indication when both last mentioned relays are energlzed; and means at said first location for indicating the condition of said signal at said second location, said means operating in accordance with the energized condition of said second reverse front contact repeater relay.

8. in a railroad trafiic controling system, in combination, a section of railway track extending between a first location and second location; a traffic controlling device at each said location for controlling the movement of traffic over said track section, each said device being capable of giving a stop indication, a caution indication, and. a proceed indication, means at said second location for supplying to the rails of said track section pulses of energy of a certain polarity at a first code rate, or pulses of energy of said polarity at a second code rate, or pulses of energy of a polarity opposite to said certain polarity; code following relay means connected to the rails of said track section at each said location, each said means including two polar biased relays arranged in series opposing relationship; means including said code following relay means at said first location selectively responsive to said first two mentioned pulses for controlling the caution and proceed indications respectively of said traffic controlling device at said first location and to said third mentioned pulses for controlling indication means at said first location for indicating the condition of said traffic controlling device at said second location; means at said first location for supplying to the rails of said track section, during the off periods of said pulses supplied to the rails at said second location, pulses of energy of a predetermined polarity, or pulses of energy of a polarity opposite to said predetermined polarity, or said pulses alternately during each successive off period of said pulses supplied to the rails at said second location; means including said code following relay means at said second location selectively responsive to said fourth mentioned pulses for energizing a track occupancy reflecting relay at said second location, and to said fifth and sixth mentioned pulses for controlling the caution and proceed indications respectively of said traflic controlling device at said second location; and a manually controlled device at said first location, said device being employed for controlling the said means at said first location for supplying to the rails of said track section said fourth, fifth and sixth mentioned pulses of energy.

References Cited in the file of this patent UNITED STATES PATENTS 2,291,579 Judge July 28, 1942 2,349,680 Shields May 23, 1944 2,360,948 Jerome Oct. 24, 1944 2,558,473 Young June 26, 1951 2,703,839 Judge Mar. 8, 1955 

